Our goal is to develop a reliable conduit (synthetic or biograft) for aortocoronary bypass for patients lacking suitable autologous veins. Factors influencing the thrombogenicity and patency of 4mm (ID) prostheses will be studied in the canine carotid and coronary arteries. In vivo effects on graft character, blood flow rate and pattern, blood composition and coagulability (untreated and altered by antiplatelet medications) will be measured. Performance assessment involves measurement of coagulum of are and thickness, as well as patency. These data will be subjected to statistical analysis.